The disclosure of Japanese Patent Application No. 2002-310649 filed on Oct. 25, 2002, including the specification, drawings and abstract, is incorporated herein by reference in its entirety.
1. Field of the Invention
The invention relates to fuel injection amount control apparatus and method of an internal combustion engine, and particularly relates to such fuel injection amount control apparatus and method that estimates an amount of fuel deposited on an intake system of the engine, and determines a fuel injection amount depending upon the estimated fuel deposition amount.
2. Description of Related Art
A known example of the above type of the fuel injection amount control apparatus is disclosed in, for example, Japanese Patent No. 2606226. The fuel injection amount control apparatus disclosed in this publication is adapted to estimate an amount of fuel deposited on a wall of an intake passage, based on a fuel behavior simulation model (or a fuel deposition model), and determine an amount of fuel to be injected, depending upon at least the estimated fuel deposition amount.
Also, after the engine stops rotating, the control apparatus disclosed in the above-identified publication estimates an evaporation speed or rate of the fuel deposited on the wall of the intake passage during a stop of the engine, and estimates the amount of fuel deposited on the intake passage wall during the stop of the engine, based on the estimated evaporation speed. Upon a re-start of the engine, the control apparatus sets the fuel deposition amount estimated during the stop of the engine, as an initial value of the fuel deposition amount used by the above-indicated fuel behavior simulation model. Thus, the control apparatus is able to estimate, with high accuracy, the amount of fuel deposited on the intake passage wall at the time of the re-start of the engine.
The above-identified publication (JP-B2-2606226) discloses that the estimated evaporation speed is a function of the intake passage wall temperature only, but does not disclose a specific method for accurately estimate the evaporation speed. Also, the fuel deposition amount on the intake passage wall, which is estimated by the apparatus during a stop of the engine, does not necessarily coincide with the actual fuel deposition amount on the intake passage wall.
Accordingly, the above-described control apparatus may suffer from reduced accuracy with which the fuel deposition amount is estimated at the time of a re-start of the engine. In this case, the amount of fuel injected during re-starting of the engine cannot be determined to be an appropriate amount. Consequently, the air/fuel ratio of the engine cannot be set to a target air/fuel ratio, which may result in deterioration of starting characteristics (such as ease of starting) at the time of the re-start of the engine, and an increase in the amount of emissions from the engine.
It is therefore an object of the invention to provide fuel injection amount control apparatus and method of an internal combustion engine, which are able to more appropriately determine the fuel injection amount upon a re-start of the engine.
To accomplish the above object, there is provided according to one aspect of the invention a fuel injection amount control apparatus of an internal combustion engine, which is arranged to start injection of a fuel when a certain engine start condition is satisfied, and stop the injection of the fuel when a certain engine stop condition is satisfied, which apparatus comprises: (a) a fuel injecting unit that injects the fuel in an intake passage that is connected to a combustion chamber of the engine; (b) a fuel deposition amount estimating unit that estimates a fuel deposition amount that is an amount of fuel deposited on an intake passage forming member that defines the intake passage; (c) a fuel injection amount determining unit that determines a fuel injection amount that is an amount of fuel injected from the fuel injecting unit, based on the estimated fuel deposition amount; and (d) a particular process executing unit that executes a particular process for making an actual fuel deposition amount on the intake passage forming member substantially equal to zero, after the engine stop condition is satisfied and before the injection of the fuel is started under a condition that the engine start condition is satisfied.
Here, the xe2x80x9cthe intake passage forming memberxe2x80x9d may include an intake pipe (including an intake manifold), an intake valve (in particular, a back face of the intake valve), an intake control valve, such as SCV, disposed in the intake passage. The actual fuel deposition amount is made equal to xe2x80x9csubstantially zeroxe2x80x9d not only when the amount is exactly equal to zero but also when the amount is equal to a certain non-zero value. The non-zero value may be determined such that a difference between the fuel injection amount determined by the fuel injection amount determining unit in the case where the fuel deposition amount is equal to the non-zero value and the fuel injection amount determined in the case where the fuel deposition amount is equal to zero is sufficiently small, and a target (desired) air/fuel ratio can be substantially achieved even if the non-zero value is treated as zero.
The xe2x80x9cengine start condition is satisfiedxe2x80x9d, for example, when the driver operates an ignition switch from ON to START while the engine is being stopped, or when a vehicle in which control is performed for effecting or stopping injection of fuel depending upon the running conditions of the vehicle after a start of the engine shifts from an operating state in which the control for stopping fuel injection is executed to an operating state in which the control for effecting fuel injection is executed. Such a vehicle may be, for example, a so-called hybrid vehicle provided with an internal combustion engine and other power source(s), such as an electric motor, or a vehicle that is provided with an internal combustion engine as a single power source and performs control for effecting or stopping injection of fuel depending upon the running conditions for the sake of reduction of energy consumption. Similarly, the xe2x80x9cengine stop condition is satisfiedxe2x80x9d, for example, when the driver operates the ignition switch from ON to OFF while the engine is being operated with fuel injected, or when the vehicle in which control is performed for effecting or stopping injection of fuel depending upon the running conditions of the vehicle after a start of the engine shifts from an operating state in which the control for effecting fuel injection is executed to an operating state in which the control for stopping fuel injection is executed.
With the control apparatus as described above, after a certain engine stop condition is satisfied and before injection of fuel is started under a condition that a certain engine start condition is satisfied (i.e., during a stop of the engine), the actual amount of fuel deposited on the intake passage forming member is made substantially equal to zero. Accordingly, upon a start of the injection of the fuel with the engine start condition satisfied (i.e., upon a re-start of the engine), if the fuel deposition amount estimating unit is arranged to start estimation of the fuel deposition amount in a condition that the initial value of the fuel deposition amount estimated by the fuel deposition amount estimating unit is set to zero (or a certain value in the case where a certain amount of fuel is injected by the fuel injecting unit during a stop of the engine), the estimated and actual values of the fuel deposition amount on the intake passage forming member obtained at the time of the re-start of the engine can be surely made substantially equal to each other. As a result, the fuel injection amount for the time of a re-start of the engine can be determined to be an appropriate value, to thereby provide a target air/fuel ratio, thus assuring improved starting characteristics of the engine upon the re-start of the engine and a reduction in the amount of emissions from the engine.
The fuel injection amount control apparatus may include a motoring unit capable of executing motoring of the internal combustion engine. In this case, the above-indicated particular process executing unit preferably causes the motoring unit to execute motoring of the engine as the particular process. Furthermore, in this case, the particular process executing unit preferably causes the fuel deposition estimating unit to estimate the fuel deposition amount on the intake passage forming member while the motoring unit is executing motoring of the engine, and causes the motoring unit to stop motoring of the engine when the estimated fuel deposition amount becomes substantially equal to zero.
When motoring of the engine is carried out, air flows into the intake passage of the engine, and the fuel deposited on the intake passage forming member is released from the intake passage forming member due to the air flow, and is drawn into the cylinder (i.e., the combustion chamber). As a result, the fuel deposition amount on the intake passage forming member decreases with time, and becomes substantially equal to zero when a certain period of time elapses.
Accordingly, with the control apparatus provided with the motoring unit for effecting motoring of the engine as described above, if the motoring unit is arranged to execute motoring of the engine during a stop of the engine, only a simple arrangement is needed for making the actual fuel deposition amount substantially equal to zero prior to a re-start of the engine, without requiring an additional device exclusively provided for executing the particular process, namely, for making the actual fuel deposition amount substantially equal to zero.
In the control apparatus provided with the motoring unit for effecting motoring of the engine as described above, the particular process executing unit preferably causes the motoring unit to execute motoring of the engine immediately after the engine stop condition is satisfied.
Generally, a catalyst, such as a three-way catalyst, is provided in the exhaust passage of the engine for removing or reducing harmful components contained in exhaust gases. The catalyst performs a good exhaust purifying or emission control function while it is in a warmed-up state. At a point of time when the engine stop condition is satisfied, the engine is often warmed up after a continuous operation thereof for a certain period of time up to the present time, and therefore the catalyst is often warmed up.
Accordingly, if the motoring unit is arranged to execute motoring of the engine immediately after the engine stop condition is satisfied, motoring of the engine is carried out while the catalyst is in the warmed-up state. Thus, when exhaust gas containing unburned components, such as HC and CO, of the fuel released from the intake passage forming member during execution of motoring flows into the catalyst, the unburned components can be favorably removed or treated by the catalyst, resulting in a reduction in the amount of emissions during execution of motoring.
In the case where the particular process executing unit is arranged to cause the motoring unit to execute motoring of the engine, and where the engine is provided with an introduction passage through which a part of exhaust gas that passes the exhaust passage of the engine is introduced into the intake passage (namely, where the engine is provided with a so-called EGR system), the particular process executing means preferably introduces the part of the exhaust gas into the intake passage through the introduction passage when the motoring unit executes motoring of the engine.
The air flowing through the intake passage and the fuel released from the intake passage forming member during execution of motoring flow into a combustion chamber defined by a cylinder, a piston and the like that have already been warmed up, so that the air and the fuel are warmed by heat of the cylinder, piston and the like, to thus provide exhaust gas that subsequently passes through the exhaust passage. Accordingly, if a part of the exhaust gas is introduced into the intake passage through the introduction passage during execution of motoring, the temperature of the intake air (a mixture of the air and the exhaust gas) passing over the fuel deposited on the intake passage forming member is elevated.
Consequently, evaporation of the fuel deposited on the intake passage forming member is promoted, and the time it takes from a start of motoring to a point of time when the actual fuel deposition amount is made substantially equal to zero can be shortened. In other words, the time required for causing the motoring unit to execute motoring of the engine can be shortened, and, if energy needs to be supplied to the motoring unit for effecting motoring, the energy consumption by the motoring unit can be advantageously reduced.
The fuel injection amount control apparatus of the engine as described above is preferably provided with a pre-start injection commanding unit that causes the fuel injection unit to inject a predetermined amount of fuel prior to a start of the injection of the fuel under the condition that the engine start condition is satisfied, after the actual fuel deposition amount on the intake passage forming member is made substantially equal to zero through the particular process executed by the particular process executing unit.
At a point of time when the injection of the fuel is started with the engine start condition satisfied (i.e., upon a re-start of the engine), the engine is not completely warmed up since it has been continuously stopped for a certain period of time up to the present time. Therefore, the fuel injected from the fuel injecting unit (e.g., the injector) is less likely to be atomized or vaporized, and the proportion of fuel that is in the form of liquid drops in the fuel flowing into the cylinder is increased. The fuel in the form of liquid drops are less likely to be burned in the cylinder as compared with the fuel that has been atomized. In this case, therefore, the amount of unburned components, such as HC and CO, in the exhaust gas is increased, and the amount of emissions from the engine is accordingly increased. It is thus preferable to reduce the amount of the fuel injected from the fuel injecting unit at the time of a re-start of the engine.
In the meantime, in the fuel injection amount control apparatus of the engine as described above, the fuel injection amount determining unit is arranged to determine the amount of fuel injected from the fuel injecting unit, based on the fuel deposition amount estimated by the fuel deposition estimating unit. Accordingly, if the fuel deposition amount estimating unit starts estimation of the fuel deposition amount upon a re-start of the engine while the initial value of the fuel deposition amount estimated by the fuel deposition amount estimating means is set to a certain value larger than zero, the amount of fuel injected from the fuel injecting unit can be reduced by an amount of fuel that is released from the intake passage forming member and drawn into the cylinder, out of the predetermined amount of the fuel deposited on the intake passage forming member at the time of the re-start of the engine.
As described above, if the predetermined amount of fuel (that is larger than zero) is actually injected after the actual fuel deposition amount becomes substantially equal to zero through the particular process and before the injection of the fuel is started with the engine start condition satisfied (namely, prior to a re-start of the engine), the estimation of the fuel deposition amount by the fuel deposition amount estimating unit is started in the condition that the initial value of the fuel deposition amount estimated by the fuel deposition amount estimating unit upon the re-start of the engine is set to the above-indicated predetermined amount, and therefore the estimated and actual values of the fuel deposition amount on the intake passage forming member can be made substantially equal to each other during re-starting of the engine. Furthermore, the amount of fuel injected from the fuel injecting unit can be reduced. Consequently, during re-starting of the engine, the fuel injection amount can be determined to be an appropriate amount, to thereby provide a target (desired) air/fuel ratio, and the amount of emissions from the engine can be reduced.
It is also preferable that the above-indicated predetermined amount in which the pre-start injection commanding unit commands the fuel injecting unit to inject the fuel is equal to an amount of fuel that is supposed to be actually deposited on the intake passage forming member at a certain point of time after the injection of the fuel is started with the engine start condition satisfied.